Beretning Nr. 96.
C. H. BORNEBUSCH:
THE FAUNA OF FOREST SOIL.
(SKOVBUNDENS DYREVERDEN).
(Særtryk af Det forstlige Forsøgsvæsen i üanmark, XI).
MCMXXX.
DET FORSTLIGE FORSØGSVÆSEN I DANMARK
udgives ved den forstlige Forsøgskommission under Redaktion af Pro- fessor A. OPPERMANN, i Hæfter sædvanlig paa 5—10 Ark, der udsendes fra Statens forstlige Forsøgsvæsen, Møllevangen pr. Springforbi. Cirka 25 Ark (400 Sider) udgør et Bind, for hvilket Subskriptionen er gældende;
Prisen pr. Bind er 5 Kr., der tages ved Postgiro samtidig med Udsendel- sen af 1ste Hæfte.
Bd. 1 ( 1 9 0 5 — 1 9 0 8 ) : Nr. 1. H . B O J E S E N : H . C . U l r i c h s Bøgekulturer.
— Nr. 2. O. G. P E T E R S E N : Nattefrostens Virkning p a a Bøgens Ved. — Nr. 3. A. OPPERMANN: Nogle Træmaalings-Forsøg, I. — Nr. 4. P . E . MÜL-
LER: O m nogle Bælgplanters Udvikling i bearbejdet jydsk Hedejord. — Nr. 5. F R . W E I S : Nogle Vand- og Kvælstofbestemmelser i Stammer af F y r og Gran. — Nr. 6. A. OPPERMANN: Egens Vækst i Jægersborg Hegn. — Nr. 7. A. OPPERMANN: Tilvirkning og Anvendelse af dansk Gavntræ, I.
— Nr. 8. F . I. ANDERSEN: Gennemhugning og Grenekapning i Rødgran. — Nr. 9. P . E. MÜLLER og F R . W E I S : Studier over Skov- og Hedejord, I. — Nr. 10. A. OPPERMANN: Rødgranens Vækst paa god, midtjydsk Hedebund.
— Nr. 11. L. A. HAUCH: Udhugning i unge Egebevoksninger. — Nr. 12.
K. MØRK-HANSEN: C. H. Schrøders Udhugning i Bøg. — Nr. 13. A.»OPPER- MANN: E n Prøveflade i Avnbøg. — Nr. 14: Forsøgsvæsenets Ordning og Ledelse.
Bd. II ( 1 9 0 8 — 1 9 1 1 ) : Nr. 15. L. A. HAUCH: Nattefrostens Virkning i ung Bøgeskov.— Nr. 16. A. OPPERMANN: Vrange Bøge i det nordøstlige Sjælland. — Nr. 17. P. E . MÜLLER og F R . W E I S : Studier over Skov- og Hedejord, II. — Nr. 18. J O H S . H E L M S : Forsøg med Lystræer paa Feld- borg Skovdistrikt. — Nr. 19. A. OPPERMANN: E n Prøveflade i Rødeg. — Nr. 20. A. OPPERMANN: Tilvirkning og Anvendelse af dansk Gavntræ, II. — Nr. 2 1 . A. H O L T E N : Brud i staaende Granstammer. — Nr. 22—24. For- søgsvæsenets Ordning og Ledelse.
B d . III ( 1 9 1 0 — 1 9 1 3 ) : Nr. 25. P. E . MÜLLER, K. RØRDAM, J O H S . HELMS,
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Bd. IV ( 1 9 1 2 — 1 9 1 5 ) : Nr. 28. A. OPPERMANN: Højdelag i Bøgebevoks- ninger (Höhenschichten in Buchenbeständen). — Nr. 29. A. OPPERMANN:
Ædelgranens Vækst paa Bornholm (Le sapin pectiné å l'ile de Bornholm).
— Nr. 30. A. OPPERMANN: Den grønne Douglasies Vækst i Danmark (The Douglas Fir in Denmark). — Nr. 3 1 . L. A. HAUCH og F . KØLPIN RAVN:
Egens Meldug (L'oidium du chéne). — Nr. 32. A. OPPERMANN: En Gran- bevoksning paa god, midtjydsk Hedebund (Ein Fichtenbestand auf gutem Heideboden im mittleren Jutland). — Nr. 33. A. OPPERMANN: Overvintring af Agern (Überwinterung von Eicheln). — Nr. 34. J O H S . H E L M S : Iagt- tagelser over Rødgranens og Ædelgranens ydre Form (Beobachtungen über die äussere F o r m der Fichte und Weisstanne). — Nr. 35. A. OPPERMANN:
Elleve Prøveflader i Bøgeskov (Elf Probeflächen in Rotbuchenbeständen).
— Nr. 36. J O H S . HELMS: Forsøg med Lystræer paa Feldborg Skovdistrikt, II (Versuche mit Lichthölzern auf Heideboden). — Nr. 37. L. A. HAUCH:
Proveniensforsøg med Eg (Provenienzversuche mit Eiche). — Nr. 38. F R . W E I S og C H. BORNEBUSCH: Om Azotobacters Forekomst i danske Skove,
rorsvaret finder Sted Torsdag den 22. Maj 1930 - Kl. 2 i Auditorium A, Universitetets Anneks, Studie- stræde 6 o. G.
THE FAUNA OF FOREST SOIL
THE FAUNA
OF FOREST SOIL
S K O V B U N D E N S DYREVERDEN
BY
C. H. B O R N E B U S C H
ü tø
WITH 7 FIGURES IN THE TEXT AND 28 PLATES
COPENHAGEN
PRINTED BY NIELSEN & LYDICHE (AXEL SIMMELKIÆR)
MCMXXX
Denne Afhandling er af det matematisk-naturvidenskabelige Fakultet antaget til offentlig at forsvares for den filosofiske Doktorgrad.
København, den 2. April 1930.
J. F. STEFFENSEN,
h. a. dec.
C O N T E N T S
Indholdsfortegnelse
Preface Page 1 Introduction » 2 Choise of Method and Materials » 9 Detail Investigations » 25 Description of the Animals, their Life and Habits » 83 Localities compared » 125 Intensity of Animal Life » 138 A Retrospect of Results » 148 Bibliography » 154
S k o v b u n d e n s D y r e v e r d e n
Indledning Side 159 Valg af Metode og Materiale » 161 De enkelte Undersøgelser » 167 Beskrivelse af de fundne Dyr og deres Levevis . . > 187 Sammenligning af Lokaliteterne » 200 Dyrelivets Intensitet » 212 Tilbageblik over Resultaterne » 220
Reprinted from Det forstlige Forsøgsvæsen i Danmark vol. XI.
P L A T E S
Billedtavler
I. Locality 10. Oak, Mull, Mercurialis. Eg, Muld, Bingelurt.
II. Locality 15. Beech, Mull, Anemone-Asperula. Bøg, Muld, Anemone- Bukkar.
III. Locality 5. Beech, Mull, Melica-Asperula. Bøg, Muld, Flitteraks- Bukkar. ,
IV. Locality 9. Beech, Mull, Oxalis. Bøg, Muld, Skovsyre.
V. Locality 2. Beech, Impoverished Soil, Polytrichum. Bøg, forarmet Bund, Skovjomfruhaar.
VI. Locality 4. Beech, Raw Humus, no Flora. Bøg, Maar, ingen Flora.
VII. Locality 20. Beech, Raw Humus, no Flora. Bøg, Maar, ingen Flora.
Locality 7. Vaccinium myrtillus. Blaabær.
VIII. Locality 1. Spruce, Mull, Oxalis. Gran, Muld, Skovsyre.
IX. Locality 6. Spruce, Raw Humus, Moss Cover. Gran, Maar, Mos.
X. Locality 8. Spruce, Raw Humus, Moss Cover. Gran, Maar, Mos.
XI. Soil Sections from Localities 15 and 9. Jordbundsprofiler fra Lokaliteterne 15 og 9.
XII. Soil Sections from Localities 2 and 4. Jordbundsprofiler fra Lokaliteterne 2 og 4.
XIII. Soil Sections from Localities 1 and 6. Jordbundsprofiler fra Lokaliteterne l og 6.
XIV. Leaf and Raw Humus Layer from Locality 4. Løv- og Maarlag fra Lokalitet 4.
XV. Moss-Needle and Raw Humus Layer from Locality 6. Worm Casts from Beech Mull. Mos-Naalelag og Maarlag fra Lokali- tet 6. Regnorme-Ekskrementer fra Bøgemuld.
XVI. Needle Layer and Surface Mull from Locality 1. Naalelag og Overflademuld fra Lokalitet 1.
XVII. Snails, Spider, False Scorpions and Insects. Snegle, Edderkop, Mosskorpioner og Insekter.
XVIII. Centipeds, Milliped and Trichoniscus. Skolopendere, Tusindben og Bænkebider.
XIX. Millipeds and Scutigerella. Tusindben og Scutigerella.
XX. Mites. Mider.
XXI. Mites. Mider.
XXII. Collembola. Springhaler.
XXIII. Crane-flies. Stankelben.
XXIV. Diptera Larvae. Larver af tovingede Insekter.
XXV. Diptera Imago and Larvae. Imago og Larver af tovingede Insekter.
XXVI. Beetles and Earwigs. Biller og Ørentvis te.
XXVII. Beetles and Saw-fly. Biller og Bladhveps.
XXVIII. Beetles and Beetle Larvae. Biller og Billelarver.
PREFACE.
1 he idea of studying t h e fauna of forest soil in o r d e r to gain a thorough knowledge of its organization under varying conditions, has of late years been borne in upon me during my studies of the different types of forest soil in relation to their flora and soil- condition, and t h e decomposition of organic materials under the influence of microorganisms. It was quite natural to suppose that the fauna also would vary in organization from place to place according to types of forest soil. The following investigation will show to what extent this theory proves correct.
When the idea had become quite clear to myself, 1 laid it before Professor Dr. A. OPPERMANN, Director of T h e Experimental Forestry Service, who kindly approved of my pursuing t h e subject, carrying out a part of t h e work in t h e laboratory of the Service, whereupon, recommended by Professor OPPERMANN and Professor WESENBERG-LUND, I applied to T H E CARLSBERG FUND, which accorded me a subsidy to defray the expenses for instruments, journeys, and assistants. While engaged upon t h e work I received t h e kind assistance of several zoologists, who settled for me questions of species, etc. In ascertaining the diptera and other insects respectively, I am especially indebted
to Mr. W. LUNDBECK, Inspector, and Mr. K. L. HENRIKSEN, M. S C , of the
Zoological Museum, Copenhagen; but also to Mr. BRÆNDEGAARD, M. A.;
Mr. H J . DITLEVSEN, M. S C ; Mr. H. FASMER, Student of Nat. S c ; Mr.
P. HAMMER, M. S C ; Mr. VICTOR HANSEN, J. P.; Mr. KRYGER, Municipal
School Teacher; Mr. MALTBÆK, M. A.; T h e Librarian, Mr. P. NIELSEN;
Mr. K. STEFFENSEN, M. S C ; and Mr. S. L. TUXEN, Student of Nat. S c ,
all of Denmark; T h e Reverend HILDERIC FRIEND, Solihul, England;
The Reverend KNEISSL, Oberalting, Bavaria (Bayern), and Mr. SCHENKEL, L. L. D., Basel, Switzerland.
I take this opportunity of tendering T h e Experimental Forestry Commission, t h e Directors of The Carlsberg Fund, as well as all t h e
Det forstlige Forsøgsvæsen. XI. 28. Marts 1830. J
2 [2]
gentlemen mentioned above, my sincerest thanks. I also desire to thank F. Hendriksen's Studios for the careful production of the plates, and to express my appreciation of the work performed by the two young ladies who have been my assistants: first, for six months, Student Miss VITA BAARCK, and next, for eighteen months, (now) Mrs. ASTA BRINKEL, who both worked assiduously and carefully for three hours every day in sorting and counting the great number of animals collected.
Introduction.
How many people, in passing through the forest, have any idea of the life teeming under their very feet, every plot of ground that they tread upon being alive with an immense number of small animals. It constitutes a world of its own, unobserved by our eyes. We see the roedeer and the h a r e ; sometimes, especially towards dusk, we encounter the fox and the badger; we enjoy the singing of birds and watch with pleasure their activities; admire the birds of prey soaring majestically above our heads; observe the little squirrel as it nimbly skips from tree to tree. On closer observation we shall also catch sight of a timid little mouse, a frog hopping off and vanishing like a brown shadow, a little snail or a beetle crossing the forest path or crawling up a stem; and the butter- flies, fluttering among the trees, are well known to us. But the abundance of life beneath our feet, we shall discover only by lying down and looking closely among the leaves, herbs, and grass. Then, descending to animals of a class far smaller in size, we shall be fairly taken aback by the profusion of animals disclosing themselves to our view. If we pick up a little bunch of leaves or a tuft of moss, we shall see a great number of animals, crawling and leaping out, so small that it is impossible for us to follow them with our eyes.
If we wish to study this particular fauna a little more closely, take along home a bunch of leaves, and in our room try to collect all the animals to see how many there are, we shall soon find that it is a most difficult task. A couple of sprightly beetles trying to escape across the table, are soon captured; some small red earthworms and white potworms, as also some white or gray grubs of two-winged insects do
[3] 3 not give much trouble either; with a wet hair-pencil we intercept a few of the largest mites, about one millimeter in length; with greater difficulty we catch some of the small bustling springtails, while others once more make their escape from the wet hair-pencil and disappear. After a great deal of trouble we finally succeed in collecting some of the larger specimens, but find that the leaves still contain no end of vivacious animals so small t h a t we can hardly distinguish them, and in spite of all our pains we have to give it up.
A thorough knowledge of the subject we shall not gain in this way, therfore we must resort to other methods, to which we shall return in due course.
Let us, however, first try to understand what interest, apart from satisfying our curiosity, we may have in getting to know these tiny animals of the forest soil, not their names only, but their numbers and habits as well.
In woodlands it is of only rare occurrence that we plough or harrow, weed or hoe; often we do not even sow or plant, but leave the soil undisturbed. We subject our stands to no other care t h a n that of thinning, which, at any rate, is the main thing. If the soil undergoes a tilling process it is only at intervals of m a n y , m a n y years, and this only in case the soil is supposed to be too deteriorated for natural regen- eration, or in case we wish to produce a stand of another species, not content, thus, with the natural regeneration of the old stand.
During these long periods the forest regulates itself, just like the primeval forest from time immemorial, and requires no artificial attention with the sole exception of thinning, which, moreover, causes traffic on the ground. At any rate, this should be the rule, but it must be admitted that m a n ' s encroachments upon nature have often made havoc of the naturally prevailing good condition of the soil. How is it poss- ible, it may now be asked, t h u s to leave the forest soil to take care of itself?
The forest is of a very composite structure. It consists not only of trees, Under the tall trees we find undergrowth and s h r u b s ; the soil is covered with herbs and grasses. All these penetrate the earth with their roots, smaller plants near the surface, trees often to great depths. The leaves of
4 [4]
trees and dead branches, the stalks and leaves of the soil flora, fagots left by the woodcutters — all this residue moulders on the forest ground; the carbon and hydrogen, by a slow process of combustion, are transformed into carbonic acid and water; the nitrogen is released as ammonia, which is often retransformed into nitric acid. The salts are released and, by means of rainwater, transferred to the roots in the ground, and in this way nitrogen and nutritive salts are once more absorbed by the plants. True, some of the salt is washed away, much nitrogen is lost in the air, but the roots of the trees carry other salts from the deeper layers of earth, and divers micro- organisms absorb fresh nitrogen from the air; otherwise, all forest plants, from the tallest tree to the smallest herb, would suffer from want of nourishment. This process goes on »of its own accord« without either work or care on the part of the forester, but not always equally well. If the various processes of decomposition are to lake the most favourable course, and the trees are to grow as much as possible, all the factors working together to these ends must be brought to contribute to the utmost of their capacity, and one of these factors is the fauna of the forest soil.
Just as the farmer has to cultivate his field with plough and harrow, partly to render the soil friable, partly that the decaying manure may be covered with earth, so the soil in the forest must be subjected to mechanical cultivation that it may keep friable and porous, suitable to the plants, and also that organic residue m a y be decomposed, and to this end a mechanical work is required; this is to be effected by creatures capable of moving about, i. e. by animals. But these do not confine their work to t h i s ; they decompose leaves and branches, bite them into small bits, let the organic material pass through their intestinal canal, thus making it more easily accessible to the bacteria and fungi by the aid of which the final process of mull formation and the chemical combustion of the materials take place.
Foresters have for centuries been aware of the part played by big m a m m a l s , especially domestic animals. They knew how to benefit by pigs rooting up the forest ground, thus improving and preparing it for the lodging of the falling mast and furthering the natural regeneration of the
[5] O
forest. But cattle, too, would often be useful in preparing the soil by the tread of their hoofs and by tearing loose the grass; especially, when forest areas, which had been used as pasture, were hedged in, an excellent young forest would often grow up. Also horses, sheep, goats, and deer may indeed prove equally useful in these respects, but the benefit is greatly counterbalanced by the damage caused by these animals, because they devour the bark and the young trees most voraciously, while cattle so m u c h prefers grass to tree plants that a moderate grazing may be beneficial to the young growth of trees. In Lüneburger Heide great areas were in times past successfully sown with pine seed, which was then trodden down by large flocks of sheep.
All herbivorous animals, in transforming vegetable matter into manure, would of course so far seem to be useful to the soil, but too much grazing, taken together with the damage done to the undergrowth and the shrubs, which are to provide shelter in the forest, has proved to be detrimental to the good condition of the soil.
Badgers and foxes, within the limited areas of their burrows, very thoroughly prepare and fertilize the soil, activities resulting not only in a particular soil flora, but sometimes even in another species of trees (ash) than the surrounding woodland (BORNEBUSCH 1923, p . 105). To the mole, a regular inhabitant of the soil, wre shall return later on. To a smaller extent, mice, shrews, toads, and other small verte- brates, are good tillers of the topsoil. In other parts of the world various rodents play an important part in the pre- paration of the soil.
The direct influence on the forest soil as caused by birds is far smaller than that of mammals. The scratching of hens on the borders of the forest is often detrimental to the soil, because the leaves are stirred u p and carried away by the wind, and the earth is left compact and deficient in mull;
in sheltered parts, on the other hand, we may sometimes witness that the scratching of hens is conducive to regeneration.
Crows, blackbirds, and other birds turning the leaves and the moss in hunting for caterpillars and w o r m s , are no doubt frequently of importance in lodging the seed where it is best capable of germinating. But otherwise, the chief importance
6 [6]
of birds to the forest is mainly to be found in their checking the noxious insects, and in their eating and spreading of seed.
They can indeed do much damage by eating the seed, but especially the j a y , and also ducks, pigeons, and other birds have, on the other hand, greatly influenced the migration of species bearing heavy fruits, chiefly the oak and the beech, and have in this way proved a cultural factor of incalculable importance.
The idea that also the little animals living in the soil are useful, is traceable to W H I T E (1789), w h o advanced the view, remarkably correct for his time, that the condition of the soil and the thriving of the plants are largely due to the influence of worms. His statements, however, seem to have been passed by rather unnoticed, while DARWIN'S studies, which appeared half a century afterwards, gave rise to further investigations, resulting in an extensive literature, of which we shall mention the following: DARWIN (1840, 1881), HENSEN (1877, 1882), MÜLLER (1878b, 1884, 1887, 1889, 1894), BOAS (1882), TUXEN (1882), W O L L N Y (1890, 1897), RIRAUCOURT & COMBAULT (1907).
We have learned how worms c a n y the plant residues into the soil, where they subsequently devour it, and h o w they constantly deposit, on the surface, layers of good earth in form of excrements (worm casts); in this way, moreover, the stones sink below the layer of earth thus prepared by the worms and kept light and friable through their work. KEILHACK
describes (1899) how tiger-beetles, scarabees, ants, burrowing wasps, etc., by their excavations in sandy soil, effect a similar kind of sorting process, thus bringing the fine earth up to the surface.
The realization of the part played by animal life has been gradually growing for the last fifty years. T h e theory formerly prevailing may be expressed by the following quotation from BREHM & ROSSMÄSSLER (1867): »Now as to the salutary influence of the inferior animals on the forest, this can of course only be an indirect one, through the extermination of animals detrimental to the forest.« It is not till SCHIODTE'S
dissertation (1875) and MÜLLER'S » S t u d i e r o v e r S k o v j o r d « i . e . studies of forest soil (1878b, 1884; in German 1887; in French 1889) that the fauna of forest soil is referred to as a matter of interest. T h e latter work shows how it varies
[7] 7 according to condition of soil, and how good mull seems to be contingent upon earthworms. The views touched upon by the author made but little headway; in forest-zoological textbooks it is almost exclusively noxious animals and their foes that are dealt with. An exception to this is D a n s k F o r s t - z o o l o g i by BOAS, for already in the first edition, 1896—98, the author mentions the earthworms (1896—98, p. 418, and 1923, p. 723); and their activities as salutary to the soil are also dealt with in textbooks on Danish forestry (HAUCH &
OPPERMANN, 1898—1902, p. 18 ff.).
Foreign investigators of forest soil, however, have gradu- ally come to realize the importance of terricolous fauna, e. g.
RAMANN, whose interest was aroused by the works of MÜLLER,
with which he was well acquainted, and w h o , in his »Boden- kunde« (1895, 1905; 1911 a) refers to the fauna of the soil.
He writes (1911 b, p. 164) as follows: »Though as yet we have no definite opinion about the importance of the various animals to the transformation of the soil, we have every reason to further all that conduces to the development of the lower fauna and to ward off everything that m a y be detrimental to it. T h e derangement of the equilibrium of the natural factors through encroachments on the part of man has probably always proved detrimental.«
Of late years, indeed, a great deal has been written about the fauna of the forest soil, but thorough investigations are scarce. T h u s RAMANN (1911 b) published some figures, in which however he distinguished between »Regenwürmer« (earth- worms) and »Kleintiere« (smaller fauna) only. For ascertaining the number of the former, the samples are too small, and as the animals have only been picked off the earth, and no definite limit downwards is given, the numbers stated furnish but little information. For earthworms so big that, at any rate in mully soil, they can be picked off with approximate accuracy by merely searching the soil, earlier as well as later investigations as to their number and activities are not wanting.
T h e small species of earthworms living in raw h u m u s are difficult to find; hence the wrong view advanced that it is entirely devoid of earthworms (MÜLLER, 1878 b , p. 44). My investigations go to prove that, all in all, raw h u m u s is far more abounding in animal life than was formerly supposed.
[8]
Objective studies of the fauna, including very small animals, have been made by the Indian, PILLAI (1922) and by v. P F E T T E N
(1925), both of ESCHERICH'S laboratory, Munich (München), in pine and spruce forests respectively, though in the litter only, and the smallest animals, springtails and mites, have not been counted. An investigation by SOUDEK (1928), too, confines itself to the litter. In this way, for instance, only a small part of the important earthworms will be included. D O G I E L
and E F R E M O F F (1925), on the other hand, have made a fair attempt to collect the entire fauna of the soil; true, they have only picked out the animals, but that this work has been done with painstaking care, appears from the great number of mites and springtails. It has been interesting to compare the four investigations from coniferous woods last mentioned with results from similar types of forest soil in Denmark. In Sweden, both SCHOTTE and HESSELMAN have emphasized the desirability of getting the Swedish Experi- mental Forestry Service to undertake an examination of the fauna of the forest soil (Meddelanden från Statens Skogs- försöksanstalt, vol. 12, pp. 48 and 56), and some researches by TRÄGARDH have appeared (1928).
From the facts mentioned above we learn that there is practically no material from which it is possible to form an idea of how the fauna of the forest soil is organized under various conditions.
From his childhood the author has been acquainted with MÜLLER's investigations, and ever since his years of silvicultural training has keenly felt the deficiency in knowledge as regards the fauna of the forest soil, a chief factor in the natural economy of the forest. While for a decennium engaged upon the study of the various types of flora according to their respective soils, he became desirous of subjecting the fauna to a thorough examination as well. A study of the macro- scopic fauna of the forest soil then presented itself as one of the domains where an effectual study was possible, this task being ever so much easier of accomplishment than for instance the study of the microorganisms of the soil, that it is rather surprising that our knowledge in this province has so long remained quite fortuitous and fragmentary.
Choice of Method and Materials.
While the forest plants, when we confine ourselves to the fanerogames, ferns, and mosses, are comparatively easy to survey; the animals, hecause of their locomotion, are more difficult to study. The trees we can count as well as measure;
as for shrubs and young trees, it is, at any rate, practicable to make out the approximate areas covered, as also their ages and heights. Herbs, grass, and moss, plainly indicate which types of flora dominate the ground in different areas;
and, if we should be desirous of entering into further partic- ulars, we can roughly estimate in w h a t proportions the various species of plants cover the ground, or we can ascer- tain their quantity statistically by the aid of small sample plots, and thus gain an objective representation of the organi- zation of the flora.
Not so with the mobile animals. Domestic a n i m a l s , which in former times used to play an important part in the forest, but now in this respect are of rather small significance, we can easily control, at least in the small forests of Denmark.
In the case of deer, in an enclosed park without thick under- growth, we can form a long cordon of m e n across the entire wood, and, while proceeding from one end to the other, count the animals as they retreat through the cordon. To count the deer in unenclosed areas is, of course, more difficult, but the huntsman daily scouring the forest is generally familiar with each herd of game; hence we possess reports from old times about the quantity of game in the royal forests. The hunts- man, well acquainted with the localities, will also be able to state the approximate number of foxes and badgers, because he knows how many burrows are occupied; and, where there are not too many hares, it is also possible, though with greater difficulty, to calculate their n u m b e r approximately.
The number of breeding birds of prey, as also of rooks and crows, he will be able to ascertain; but at that the possibility of any direct estimate as to number of animals, must stop.
The smaller animals are too apt to evade detection. Two methods of ascertainment are patent in dealing with them.
One is a merely relative method (DAHL 1921): If thus, at the same time of the year and the same hours of the day, as
10 [10]
also during the same kind of weather, we pay a visit to the various parts of the forest, noting down all the birds we see or hear while crossing the area for a fixed number of hours, we shall get some idea as to what parts are relatively most abounding in birds, and also about their composite character in the various forest types. Corresponding relative estimates may be drawn by watching the results of mouse-catching in traps, or, in case we pursue entomological studies, by using a catcher among the plants at definite periods at the same hour of the day, by knocking down insects from branches, e. g. the noxious larvae infesting the oak, or by setting beetle- traps, i. e. j a r s sunk in the earth and provided with bait. If the holes we dig in the forest in order to examine the soil, are left over night, these will also serve as traps for beetles, frogs, salamanders, shrews, etc., and furnish us with a n idea of how these animals differ from one place to another.
There are other methods, however, by which it is possible to attain a better estimate as to quantities of animals. PALMGREN
(1929) has calculated the birds in Finland by researching limited areas and in this way attained approximation to the total number. In a similar way I have counted up the birds in an area at times when they sing most vigorously. The absolute numbers we can only ascertain, when the animals are so small, so numerous, and so slow in their movements, as to make it possible to take a sample of the soil and examine everything it contains. In this way did deep sea explorers, as early as 1896, examine the fauna of the sea beds by taking up samples of Vio m2 (BOYSEN JENSEN & J O H S . P E - TERSEN, 1911), a study so important to the appreciation of the food resources of fishes, e. g. the plaice; thus also we may take samples of the forest soil and examine them. As m a y be imagined, regular statistical investigations of this kind are con- fined to worms, insects, and other smaller animals. Even of the larger species of beetles for instance, the individuals are so sporadic that no information is obtainable in this way. Such an important occupier of the soil as the mole is, of course, outside the range of direct counting. The main body of fauna living in the earth, however, may be examined by m e a n s of samples of the soil. These small animals may be divided into three groups, each of which must be treated differently.
[11] 11 The method of collecting annelids, insects, myriopods, spiders, mites, etc., is based upon the fact that these animals, when the sample is subjected to a heating and desiccating process, leave it of their own accord. To this end various devices have been constructed, of which (p. 21) we shall mention only TULLGREN'S apparatus (TULLGREN, 1918), which has been taken as a model in the present investigations.
Larger worms and insects, etc., m a y simply, as formerly done by RAMANN and others, be picked off when the sample is searched, but this method is slow and inaccurate, and is only to be recommended in the case of earthworms, and even of these to the exclusion of the small species in raw h u m u s .
The next group comprises the microscopically small worms, the nematodes. These do not leave the soil when it is heated and desiccated, but encyst themselves; hence they must be separated from the soil by means of water, either by placing a compact clod of earth (sod, raw humus) in a shallow' bowl of water, in which case the nema- todes will swim out at the bottom of the bowl, there to be fished out under the microscope, or the earth (mull and mineral soil) may be washed out in water, the heavy parts are left to settle, and then the water is filtered through a fine strainer (miller's gauze), in which the nematodes, floating in the water, will be caught (COBB, 1918).
Finally, the protozoa, the minute unicellular animalcula:
to ascertain their quantity is connected with great difficulties, the result being obtained only by a diffusion just as we do with bacteria, if we are not to be content with a merely super- ficial examination through the microscope. According to
MÜLLER (1884, p. 71 ff.), testaceous rhizopods are very numer- ous in raw humus, while scarce in mull.
The first of these groups is undoubtedly of chief import- ance to the soil in making the topsoil friable and in devour- ing the residual products of plants or biting these into small pieces. (»The microscopic fauna . . . . can hardly, to any great extent, reduce the density and compactness of the mass«, MÜLLER, 1884, p. 74), and, being moreover the one most easy of access, it will, naturally, engage our atten- tion first. Hence, the following pages are mostly confined to
12 [12]
a statistical investigation of what the forest soil contains of the fauna comprising the first group, a description of the number of animals, their quantities according to weight, etc., while the possible examination of the nematodes and protozoa must be deferred till some other time.
Neither time nor subsidies have been sufficient for a closer study of the life of the different kinds of animals and their im- portance to the soil; in these respects I must at present confine myself to references to the works of others; but, in my opinion, the statistical survey here furnished, giving information as to what animals so abound in the earth as to be considered of essential value to the same, constitutes the basis needed for the study of the part played by the fauna of the soil.
Denmark is a low country, in which level or slightly undulating plains alternate with hilly moraines, which hardly ever rise to 100 m above sea level; parts of the interior of Jutland, however, are somewhat higher, rising to as much as 172 m. Loose clayey, gravelly, or sandy layers, deposited during the glacial period, most often at considerable depths, cover the substrata from the tertiary and cretaceous periods.
The clayey lands often contain a great quantity of carbonic lime, which the ice, in scouring across the layers of calcareous formations, packed into the masses of earth conveyed by the ice from the Scandinavian mountains; in some places along the shores the calcareous formations will appear as cliffs.
Unique is the island of Bornholm, consisting of primitive rock and old formations, mostly covered, however, by depos- its from the glacial period.
N. E. Sealand, north of Copenhagen, from which part most of the samples are taken, is a very hilly moraine country, where sandy and clayey lands alternate; its position is about 56° northern latitude and 12—12Va0 longitude, east of Greenwich.
The climate is characterized by Denmark's proximity to the ocean and the Gulf Stream, a fact most often resulting in mild winters and rather cool summers, as also in precipitation quite copious in proportion to temperature, all of which con- duces to a pronounced humid climate, as it also appears from the extensive raw h u m u s and podsol formations, and
[13] 13 from the fact that carbonic lime, even on clayey lands, has mostly been washed out of the upper soil layers as deep as the lowest tree roots, and even deeper. Predominating westerly winds affect the shapes of the trees, and frequently prove detrimental to the condition of t h e soil, whenever they sweep through the forest.
Table I gives further particulars about temperature and precipitation, for the two years during which the investigations Table I. Temperature and Precipitation, Lille Dyrehavegaard,
near Hillerød.
Middeltemperatur og Nedbør.
Mean Temperature, Centigrade
Precipitation, in all, Millimeter January...
February . March April May June July August September October...
November December Annum....
1926 0.5 0.7 2.7 7.5 11.0 14.6 18.2 16.4 12.8 6.1 5.4 1.4
1927 2.0 0.4 4.8 5.7 8.2 12.3 17.6 16.9 12.5 8.4 2.0 -:-2.9
Normal -h0.9
^-0.6 1.2 5.6 11.0 15.1 16.6 15.6 12.5 7.7 3.4 0.7
1926 53 72 17 30 56 83 78 44 77 106
48 40
1927 70 15 48 70 40 84 107 156 74 131 50 34
Normal 43 39 46 43 43 51 76 84 56 71 56 55 8.1 7.3 7.3 604 879 663 were carried on, as also the averages for a longer period, at the meteorological station, Lille Dyrehavegaard, near Hillerød, this being the centre of the area where most of the samples are taken.
Thousands of years ago D e n m a r k was almost entirely covered with vast forests, but as early as one thousand years ago, at the time Christianity was introduced, a great part of the country had been brought under cultivation and was fairly well populated. T h e forests had more and more to give way to the growing population, and about three hundred years ago, wood was already becoming so scarce that the authorities had to initiate restrictions in order to protect the
14 [14]
forests. The stock of trees was insufficient, and the forests were largely used for pasture; to this came the right of the yeomen of cutting down the undergrowth, which checked the growth of the young wood. Nowadays the Danish forests are covered with a good stock of trees representing a very considerable increase, as will appear from the descriptions of localities found in the next section. T h e forests comprise only about 8 per cent of the total area of the country; twice as much, however, in N. E. Sealand, the part of chief interest in this connection, and the forests in question are mostly State property.
For the present purpose I have endeavoured to present some of the chief types of Danish forest soils, and, to this end, have chosen a great many localities more particularly described in the following section.
The primeval forests of Denmark consist chiefly of beech (Fagus silvatica L.), to the entire or partial exclusion of other trees. But there are considerable tracts of oak besides and smaller areas of ash, alder, or a mingling of various foliferous trees: oak, a s h , elm, l i m e , maple, alder, etc.
Through operations on the part of the foresters, especially during the last hundred years, extensive tracts of beech forests, mainly, in loose and sandy soil, have been transformed into spruce stands (Picea abies L.), sporadically also into Scotch pine (Pinus silvestris h.) and larch (Larix decidua Mill.). To this may be added, also from the last century, large tracts of coniferous woods on heathland (calluna heaths) and downs, particularly the vast heath areas of the sandy moraines and plains of West- and Mid-Jutland. T h e trees here grown are mostly mountain pine (Pinus montana Mill.) and spruce (Picea abies); in smaller quantities, the Scotch pine (Pinus silvestris), and a few other conifers (Pinus austriaca Höss, Pinus contorta Loudon, Picea sitkaensis Trautv. & Mey., etc.).
Our beech woods present numerous types of forest soil according to climatic and other conditions, as described in previous articles (BORNEBUSCH 1920, 1921, 1923, 1925), and here the subject will be touched upon only in broad outlines.
Where the middle-aged beech stands are properly thinned, as is the case in Denmark, and where the soil is in a really good condition, a friable topsoil with good mull and with a
[15] 15 favourable nitrification, it will be covered with a flora of typical mull herbs with but slight interspersion of grasses, or none at all. Its chief representatives are the wood anemone (Anemone nemorosa L.J and the woodruff (Aspevula odorata L.), frequently also the wood-sorrel (Oxalis acetosella L.J. On good marlaceous soil with pronounced nitrification, the flora is supplemented by a n u m b e r of other plants: larkspur (Cory- dalis cava L.J, dog's mercury (Mercurialis perennis L.J, weasel- snout (Galeobdolon luteum, Huds.,), enchanter's nightshade (Circaea lutetiana L.J etc., etc. On the other hand, on more elevated and looser grounds, in less clayey, sandy, and gravelly soil, the flora is confined to anemone, woodruff, and wood- sorrel, in older stands intermingled with the wood violet (Viola siloatica, Fr.J and the greater stitchwort (Stellaria holostea L.J. Decomposition is here a little tardier than in the more fertile soil, the upper mull being greyish or nearly black, but the ammonia released through the decomposition of the organic matter, is mostly wholly converted into nitric acid. This A n e m o n e - A s p e r u l a type is represented by Lo- calities 12, 14, and 15.
A constant breeze among the trees will often result in a thick, tough covering of melic-grass (Melica uniflora Retz.J, and decomposition is somewhat tardier, the acidity of the soil being generally greater, and only a part of the ammonia released is converted into nitric acid. Locality 5 belongs to this M e l i c a t y p e . Considerably better is the condition of the soil where millet-grass (Milium effusum L.J is flourishing, Locality 3.
If the wind sweeps the borders of the forest, the leaves will be blown away, leaving the soil deficient in mull.
T h e result will be a type with wood meadow-grass (Poa nemoralis L.J, a mully soil, but heavy and poor, or a type with waved hair-grass (Aira flexuosa L.J and hair-moss (Poly- trichum attenuatum Menz.J, where the ground is covered with a very thin layer of raw h u m u s , on the top of a slight streak of leached sand. The soil is very acid, the production of ammonia is but small, and only the minutest amount of nitric acid is traceable. To this P o l y t r i c h u m t y p e belongs Lo- cality 2.
On very loose and sandy soil, as also wherever the climate is cold and d a m p , even though the beech stand be
16 [16]
carefully tended, nitrification is tardy, and a type prevails the flora of which consists of only wood-sorrel (Oxalis acetosella L.).
T h e mull is acid and approximates a little to raw h u m u s , the topsoil is quite heavy and deficient in mull, frequently some- what leached as well; the ammonia released is only partly reconverted into nitric acid. To this O x a l i s t y p e belong Localities 9 and 21. Locality 30 is from a somewhat better type with the wood-sorrel and the anemone, the O x a l i s - A n e m o n e t y p e .
If the forest has been carelessly tended, thinning neglected, and the ground exposed to winds, it will often be covered with raw h u m u s resulting from the leaf layer of the beech, fre- quently as a 8 —10 cm deep layer on a leached sand. Locality 4 is a beech raw h u m u s of the M a j a n t h e m u m t y p e , developed on the A s p e r u l a t y p e . Locality 20 is a tardier raw h u m u s of the T r i e n t a l i s t y p e developed on the O x a l i s t y p e .
Under oak stands (Quercus pedunculata Ehrh.) we often meet with a luxuriant flora of herbs and grasses. Especially on marlaceous soil the ground may be covered with dog's mercury, anemone, raspberry, tall grasses, etc., and nitrifica- tion is very brisk, as in the case of Locality 10.
It is quite a different matter if the oak stand has a thick undergrowth of young beech, as in Locality 22. In t h a t case there is no flora, but a thick layer of leaves, decomposition is slow, and the soil is mainly influenced by the dense young beech undergrowth.
T h e unmixed oak forest, even on poor ground, apart from a single type with Quercus sessiliflora Salisb. and bilberry, will preserve the mull soil, as in the case of Locality 23, a young oak plantation on poor sandy heathland. The forest is still young and dense; accordingly, there is as yet no soil flora, which otherwise on poor sandy soil usually consists of plants characteristic partly of mull, partly of raw h u m u s : Anemone nemorosah., Stellaria holosteah., Convallariamajalis'L., Luzula pilosa L., Aira flexuosa L., etc. etc.
Under other light broadleaved trees, e. g. the ash (Fraxinus excelsior h,), as under the oak, we may find a very exuberant flora. Locality 16 is from an ash stand on very rich calcareous mull, with nettle (Urtica diocea h.), dog's mercury (Mercurialis perennis L.), and goutweed (Aegopodium podagraria L.).
[17] 17 On fertile soil our spruce woods are distinguished by
mull covered with a layer of needles, and in forests of middle age the ground will mostly become covered with a dense flora of the Ox a l i s t y p e , as in Locality 1.
On loose a n d sandy soil, corresponding to the b e e c h - O x a l i s t y p e , a thick layer of r a w humus is often developed under spruce, and the ground is thickly covered with mosses:
Hylocomium triquetrum L., H. proliferum L., H. parietinum L., Hgpnum purum L., Stereodon cupressiformis L., Dicranum scoparium L., Polytrichum attenuatum, Menz., etc. To this type belong Localities 6 and 8, and the stand of mingled spruce and larch, Locality 11. Under pines, on similar soil, the ground will be thickly covered with bilberry: Localities 26 and 27;
but not where there is spruce undergrowth: Locality 28, or beech undergrowth: Locality 29. All these 7 Localities belong to the M y r t i l l u s t y p e (CAJANDER, 1909, p. 60).
Locality 7 is from a small hill covered with bilberry and surrounded on all sides by spruce.
On heathland of inferior quality — the V a c c i n i u m t y p e
(CAJANDER, 1909, p . 104) — we find raw h u m u s and moss in spruce, but of a less vigorous growth: Locality 25 and 32;
this ground is often planted with mountain p i n e : Locality 17.
Finally a few samples — Localities 18, 24, and 31 — were taken from heathland where t h e sand is covered with a thin layer of raw h u m u s with a growth of heather (Calluna vulgaris h.), crowberry (Empetrum nigrum L.), lichens (Cladina species), mosses, etc., and the soil is more or less podsolized. Locality 19 is taken under a juniper in t h e heath.
Seven of the most important of these localities have been constantly registered for two years. To these have later been added Nos. 10, 15, and 20, thus furnishing us with ten main localities, as follows:
No. of Locality
15 5 9 2 4
Species Beech
Type of Flora Kind of Soil Mull
» Impoverished
Raw Humus
» Melica-Asperula
» Oxalis
» Polytrichum
» No Flora (Majanthemum type) Anemone-Asperula
Melica-Asperula Oxalis Polytrichum
No Flora (Majanthemum type)
Det forstlige Forsøgsvæsen. XI. 25. Marts 1930.
2
18 [18]
No. of Locality
20 10 1 6
Species Beech
Oak Spruce
3>
Type of Flora No Flora (Mgrtillus type)
Mercurialis Oxalis Hylocomium (Myrtillus type)
Kind of Soil Raw Humus
Mull
» Raw Humus
The following localities, moreover, have been examined some few times:
Species Type of Flora No. of
Locality
14 Beech Anemone-Asperula 22 Oak with No Flora
Beech Undergrowth (Anemone-Asperula type)
Kind of Soil Mull
Only once have samples been taken from the following localities:
No. of Liocalit;
12 3 30 21 23 16 11 25 32 26 27 28 29 17 19 7 18 24 31
Species Beech
»
7>
Oak Ash
Spruce and Larch Spruce
» Scotch Pine
»
Type of Flora Anemone-Asperula
Milium Oxalis-Anemone
Oxalis No Flora Urtica-Mercurialis
Hylocomium (Myrtillus type) Hylocomium (Vaccinium type)
» Myrtillus
» Scotch Pine with Beech »
» » » Spruce » Mountain Pine No Flora
(Vaccinium type) Juniper
No Trees
»
»
»
Myrtillus Calluna
»
»
Kind of Soil Mull
»
»
»
»
» Raw Humus
»
»
T>
»
X
»
»
»
» The localities requiring constant registrations had to be confined to N. E. Sealand, partly with the object of facilitating
Eailiuay
S e c t F o r e s t u>ith Station, HigkroacL Lake Rivulet Town* Castle Locality Fig. 1. Map of N. E. Sealand showing numbers of localities.
Scale 1:200 000.
20 [20]
the work, partly in order to have the samples examined as soon as possible. Most of the other samples, too, were taken from these parts (see m a p , Fig. 1). Samples Nos. 17, 18, 19, 23, 24, 25 and 32 are from the heathlands of Jutland, Nos. 30 and 31 from Bornholm.
The samples were taken out in the following way:
Within a circular area of Vio mä the whole layer of leaves or needles, including the vege- tation of herbs or moss, as also dust and excrements of worms that happen more loosely to cover the ground, etc., was first removed and put into a close linen bag. The next part taken out was a 5—10 cm deep layer from the upper, porous, mull soil, of such a quality as to enable small animals to move about, and this was put into a separate bag. Finally, the lower and more compact topsoil, to a depth of 25 cm, was searched for earthworms, a number of which was often found, and for
large grubs (a few Bibio, Elater- idae, and Scarabaeidae larvae). On raw h u m u s soil, too, the layer of leaves and moss, etc., wras first taken, and then the entire layer of raw h u m u s as far as the leached sand, while neither this nor any of the layers below was examined. Even if some animals were to be found in the lower strata, they would at any rate be so few in number as to be of only minimal importance, and are therefore left out of account in these investigations. Earthworms constitute an exception. Under favourable conditions they will keep near the surface, only during dry periods in summer and hard frosts in winter will they go to considerable depths, thus evading both our investigation and their participation in the decomposition of the soil. In a few places, where it has been difficult to separate the two layers, the entire sample has been taken in one batch, e. g. on heathlands.
Fig. 2. Apparatus for driving out the animals. (1 : 10).
[21] 21 After their removal to the laboratory, either on the same day or the following morning, the samples were transferred to the apparatus designed for driving out the animals. This instrument, modelled on that of TULLGREN (1918), consists of the following parts (see Fig. 2): A large zinc funnel, sup- ported by three legs at the bottom fastened to a ring, which constitutes the basis of the instrument; the funnel is 40 cm
Fig. 3. The laboratory of The Experimental Forestx'y Service, w i t h 10 apparatuses.
high and 46 cm in diameter at the top, and has at the bottom an opening of 20 mm. In the upper part of the funnel is placed a sieve of wire netting, 42 cm in diameter; the bottom of it with 3 mm meshes; 10 cm high sides, with 6 m m meshes. Covering the whole thing, resting on the rim of the funnel, there is a 21 cm high cap of plywood, at the upper, middle part of which as source of heat is installed a carbon filament electric bulb of 35 candle-power. It is of great im- portance that the bulb does not give too m u c h heat, as this might kill the animals before they gel time to make their escape from the sample. With the candle-power used the temperature did not exceed 40° C. as long as there were any animals left. Only when the samples were thoroughly exsic- cated did the temperature in the upper part of the sample, close to the bulb, rise to 50—60° C. If the sample, while
22 [22]
still humid, had risen to this temperature, the animals might have been killed in the sieve. In order to accelerate the process of desiccation, some holes had been bored at the top of the wooden hood, an exit for the moist air.
The joint action of light, heat, and desiccation, affects the animals so as to make them move downwards, and when they have reached the bottom of the sieve, they drop into the funnel, from which they fall through the narrow opening at the bottom, and are collected in a glass containing alcohol.
Only spiders and worms may cause some difficulties, the form- er because they let themselves down by means of their own web, and sometimes make their escape, the latter because of their slimy bodies often sticking to the sides of the funnel, where they dry fast and have to be loosened with the blade of a knife.
Most of the animals leave the sample in the course of 4—6 hours. In case of large quantities of mull or raw h u m u s , however, a great number of animals may linger till the second, and even the third day, a fact proved by the replacement of fresh glasses with alcohol. The electric light was turned on only 8 hours a day. W h e n no more animals leave the sample, this is searched for chrysalides and for ani- mals that have proved too big to pass through the meshes of the strainer; this is chiefly the case with snails in shells and some large specimens of Glomeris and beetles.
The material collected is kept in alcohol until it can be sorted. T h e collembola, floating on the surface of the alcohol, are transferred to a separate glass, which facilitates the sorting.
This process takes place in the following way: In small quan- tities the material is put on a flat-bottomed porcelain dish, where, under a binocular microscope of an 8-fold magnifying power, the animals are sorted by means of a crooked dissecting needle. The sorted and counted animals are, with a fine hair- pencil, transferred to small glass-tubes, 10 X 40 m m , where they are preserved in alcohol. Each glass is numbered and lettered so as to correspond to the inventory made contempo- raneously with the counting of the animals.
The results are summarized in tables published with the following reports on the detail investigations. Before describing these, we must mention the different mistakes we are prone to make in the process.
[23] 23 By far the greatest risk of inexactitude is due to the fact that the small area of 1/io m2, even though it be selected to the best of our ability so as to represent the average for the locality, does not exactly correspond to the actual stock of animals. The fact is that the animals, of course, are not equally distributed throughout the area, many of them tending to gregariousness; this holds true, not only of the larvae of the same hatch, as for instance many diptera larvae, but also of such nimble animals as the collembola, which are often found in flocks, attracted either by some particularly enticing nourishment or by a kind of social inclination.
Whenever two samples were taken at the same time and in the same locality, the difference in the number of specim- ens of the same species often proved to be considerable.
The difference, however, was mostly quantitative only, a great similarity always subsisting between parallel samples.
It would have been preferable to have taken a n u m b e r of samples each time from the same locality as ØKLAND has done by ascertaining the number of snails (1929), but this was im- practicable if the object of our investigations was to be attained, viz: to ascertain the qualitative and quantitative differ- ences between some of the chief types of forest soil fauna. It
was requisite that samples from different localities which were to be compared, as far as possible should be taken out at the same time; hence, we had to confine ourselves to one or, at most, two samples from each, and then repeat the process in the various seasons of the year.
In the tables the annual mean for a square meter of each of the main localities has been arrived at by striking an average for each registration; where two parallel samples have been taken out, however, the mean of these has been adopted.
The formation of annual means might perhaps, theoretically speaking, appear as a somewhat incorrect procedure; and so it really would be if the fauna was altogether different, also qualitatively, in the various seasons; but this is not the case.
And yet considerable differences may obtain. Some collembola are most numerous at certain times of the year; others — even some of the chief species —, on the other hand, are numerically well represented all the year round, so that the soil teems with this group. The same holds good of
24 [24]
diptera larvae; most diptera pass through a short chrysalis and imago period in summer, but for the rest of the year are found as larvae in the forest soil; for a few species, as e. g.
Sciara (army worm), however, the larval state is but of short duration, a fact resulting in one of the main variations due to the changing seasons of the year. Enchytraeids, too, are periodically met with in great quantities, particularly profuse was their number in the wet a u t u m n of 1926 and the following mild winter. Spiders, mites, false scorpions, millipeds, centi- peds, and woodlice, are species found all the year round; so are Staphylinidae and ground-beetles (Carabidae), as well as the larvae of these. The chief beetle larvae found in the forest ground, the Elateridae larvae, retain their larval state for several years, and so we find them, big and small specimens intermingled, throughout the varying seasons. Earthworms, too, are found all the year round, active in the friable mull soil and in the layer of leaves as soon as the weather makes it possible, and the forest soil is well protected against both exsiccation and frost.
The animals do not die when the forest ground becomes frozen. They only become torpid, and revive to renewed activity when the earth thaws, and as soon as the ground is warm enough in the month of March it once more teems with animal life. I have thus found small ground-beetles (Notiophilus biguttatus) hard-frozen in the moss carpet on the frozen raw h u m u s soil in spruce woodlands, but after they had been warmed in the hand for a minute or so they ran about briskly enough.
The fauna of the forest soil thus presents both qualitative and quantitative differences during the course of the year, but is nevertheless so homogeneous that it is quite correct to use the annual mean when comparing the various types, just as we compare annual temperatures and precipitations which, from a biological point of view, must always be employed critically and with good sense.
In the main localities samples were taken out in March after the animals had revived to fresh activities, and in November after defoliation, but before the frosty season proper had set in; besides, in May and August, 1926, and in May, July, and September, 1927. This furnishes us with in-
[25] 25 formation about the quantities of animals at the times of the year in which they are active. Even though winter in Denmark is often mild and the forest ground remains frost- proof, the activity of the animals will probably be but small owing to the low temperature prevailing during such periods.
Miscalculations m a y of course also happen in case the animals, in one way or another, be lost either when samples are taken out or during transit. It is of the utmost importance to see that the animals be not squeezed or maimed, which in the apparatus would hinder them in leaving the sample; hence, the bags are to be as loosely packed as possible and the samples to be examined without any unnecessary delay. By careful management, these mistakes can be reduced to a minimum so as not to distort the actual facts presented by the fauna of the particular locality.
Detail Investigations.
In this section we pass on to examinations of the various localities and the results attained by our investigations. For each of the main localities we propose to describe in detail the stand of trees, the soil flora, and the soil, and in plates I—X at the end of the book we subjoin photographs of stands and soil flora. As for the rest of the localities, the descriptions are somewhat curtailed.
The number of animals collected are given in tables II—XIII; a column is set apart for each examination, and wherever the sample is divided into 2 or sometimes 3 layers, a separate column for each has been reserved. The scientific names of the animals, mostly the names of genera or families only, are found on the left, and the same list of names, with a few minor variations, recur in all the tables, that is to say, in different combinations the fauna is largely composed of the same elements, but in varying numbers. Further information about the individual kinds of animals and their mode of living is given in the following section, and in the plates XVII—XXVIII at the end of the book, pictures from photo- graphs taken by the author of some of the chief animals, are subjoined. The object of these pictures is to give to practical foresters and other readers with no particular zoolog-
26 [26]
ical training an idea of how these small animals look, enabling them to recognize them whenever encountered in nature. We hope that especially foresters interested in Nature, will appreciate these portraits of some of their millions of small nurslings, and that their world, in this way, wall grow more intelligible and vivid to them.
On the right in the tables will appear the annual mean of the number, an average of all the examinations being struck; where several examinations have been carried on at the same time, however, the average of these has been used in calculating the annual mean.
The next column gives in milligram (mgr.) the weight of animals per 1 square meter (ma). For several reasons — especially because the weight of the alcohol preparations is not at all commensurate with that of the living animals, and because it would have entailed an immense work to weigh the numerous specimens — it was found practically impossible to weigh all the sorted animals in order to ascertain • their exact weight. T h e approximate weight has been calculated, therefore, of each of the species, partly by having a number of samples of recently collected living animals weighed, partly, in the case of. very small animals (collembola and mites), by measurement of the mean length of a large number of individuals of each species, and a subsequent calculation of their weight, judging from the weight of larger species of the same genus and of approximately the same form. This method of ascertaining weight must of course be designated mere calculative, but the accuracy is quite sufficient for our present object, which is to gain an approximately correct knowledge of the aggregate gravity of animals in the forest soil, and to ascertain the quantitative difference obtaining in the fauna of the various localities.
Moreover, a great many casualties would in this way be equalized; for Staphylinidae and Carabidae, too, an average size has been taken for calculation, there being no special reason, in figuring out their weight, to take into account the few more straggling specimens of the larger species.
The last column, »Respiration«, the object of which is to show the »Intensity« of the animal life, we shall leave for a subsequent section.
[27] 27 First of all we shall deal with beech localities, starting with the best mull; then we pass on to some oak localities, and finally to spruce and other conifers, and heaths.
B e e c h , M u l l , A n e m o n e - A s p e r u l a . Locality 15, Table II.
The stock of trees consisting of a vigorous beech stand, 80 years old, with an interspersion of fine, tall larches (Larix decidua), 125 years old, comprises section 163 in Geels Skov
(OPPERMANN 1923, p. 146). Where the sample was taken, the ground slopes but little southwards; towards the southern edge of the wood, somewhat more. The stock of trees, which h a d been thinned in 1924/25 and 1926/27, was, after thinning in 1927 (according to report kindly submitted by The Working Plans Bureau), estimated as follows, the numbers representing hectare; among beech a little oak and maple, among larch a very few specimens of silver fir, spruce, and Scotch pine, are included:
Age Height Average diam. Stems Basal area Volume
Years m cm Number m2 m3
80 26.3 30 260 20.1 314 125 29.4 56 38 9.8 153 The thinnings of 1924/27 removed 61 m3 beech per hectare, but no larch. The annual increment for the years 1912/27 was 14.6 m3 per hectare, out of which 2.6 m3 were larch.
T h e growth of trees is thus very productive, the height of the beeches lying between the SCHWAPPACH (1912) quality class I and II. The tallest larches measured 33 m, and the thickest one had a diameter of 80 cm, breast-high.
At the place where the sample was taken out, the flora constitutes a rather close texture of Anemone nemorosa and Asperula odorata with an abundance of Stellaria holostea and some Viola silvatica intermixed. Small natural groups, 2—3 m high, of young Acer pseudoplatanus, are found in the neigh- bourhood. Under a loose layer of beech leaves, chiefly from last year's leaf fall, intermixed with some few larch needles, we meet with a friable and crumby mull, covered with a loose layer of earthworm excrements; the topsoil, too, is friable and
Species Beech Larch
